It is a general problem in geothermal exploration to extrapolate temperatures
measured in shallow depth to greater depth. It is made generally assuming steady-
state condition. Before the extrapolation topographic and paleoclimatic corrections
of temperatures must be carried out, and the effect of sedimentation, erosion and
groundwater flow must be taken into account. Additionally, the tectonic processes
must also be assessed, because they generally result in non steady-state thermal
field. In this study we present a range of tectonic processes, their thermal models
and examples how they influence the lithospheric and crustal and sediment
During extension, the lithosphere is stretched, resulting in a thinned
lithosphere. In the thermal model pure shear is assumed, which means that each part
of the lithosphere preserves its original temperature as it rises to shallower
depth due to thinning. Thus, the geothermal gradient in the lithosphere, and
consequently the heat flow increases. This mechanism is widely accepted to explain
the high heat flow in the Western Mediterranean sea, Pannonian basin and Aegean
region. The thermal model is used to calculate the thermal history of sediments and
predict maturation of organic materials.
Significant crustal extension may lead to the formation of metamorphic core
complexes. Metamorphic core complexes are middle or lower crustal rocks uplifted to
the surface as the overlying rocks are removed by extension. When the extension and
the uplift is fast the metamorphic core complexes can keep their original
temperature and geothermal gradient. As they cool or sediments are deposited on top
of them, the near surface temperature gradient and heat flow can be high, but both
quantities decrease with depth approaching the original values. Metamorphic core
complexes are frequently found in the Pannonian basin and the Aegean region and
their effect on the thermal field can be significant. Furthermore lithospheric
extension can be accompanied by (often localized) magmatism, generally resulting in
thermal advection in various levels in the crust.
Opposite to extension shortening and nape stacking reduces the geothermal gradient
and heat flow. In Europe this mechanism is mainly important in the tectonic and
thermal history of the Alps.
The tectonic processes are usually accompanied by sedimentation or erosion
modifying the thermal effects of tectonics. Sometimes a number of tectonic
processes are combined or follow each other.
For many examples in Europe it can be shown that heat flow in the crust and mantle
is not steady state. Consequently, it is not straightforward to extrapolate shallow
temperatures to greater depth or laterally beyond well control, even if the
geometry and thermal properties of basins are considered well known. Therefore, to
obtain reliable thermal models and deep temperature predictions, beyond exsiting
well control, the tectonic history of the area must be known, correct rock thermal
properties must be used, and the model results must be calibrated by measured
temperatures and heat flow data.